Bayer pixels generated by an imaging sensor typically undergo a series of steps, including noise reduction, demosaicing and color space conversion, before being compressed into a compressed video signal. CMOS and CCD imaging sensors are not fast enough to output all of the available pixels in a video frame time (i.e., 1/60th to 1/25th of a second). In order to produce high frame rate video, the pixels are cropped, binned or skipped.
Cropping is done to frame a picture per a user command and has a side effect of reducing a number of pixels output by the sensor. Binning is a process where adjacent rows and/or columns of like-colored pixels are averaged. Skipping is a process of skipping pairs of rows and/or columns of pixels. Binning or skipping is done automatically by the electronics that controls the sensor to lower a pixel rate. As less cropping is performed, more binning or skipping is performed to keep the pixel rate below a maximum level.
The FIGS. 1-4 illustrate various binning and skipping possibilities. Each of the FIGS. 1-4 illustrate how pre-binned/pre-skipped (initial) pixels are mapped into a Bayer set of post-binned/post-skipped (modified) pixels. Each of the Bayer sets is defined as two green “G” pixels, a red “R” pixel and a blue “B” pixel. To aid in explaining the illustrations, boxes and circles identify each of the red, blue and green initial pixels used to generate a corresponding modified pixel. The two green pixels in each of the Bayer sets are distinguished with a box around one G pixel and a circle around the other G pixel. The boxed green pixels in the pre-binned/pre-skipped image are used to generate the boxed green pixel in the post-binned/post-skipped image. The circled green pixels in the pre-binned/pre-skipped image are used to generate the circled green pixel in the post-binned/post-skipped image. The boxed blue pixels in the pre-binned/pre-skipped image are used to generate the boxed blue pixel in the post-binned/post-skipped image. The boxed red pixels in the pre-binned/pre-skipped image are used to generate the boxed red pixel in the post-binned/post-skipped image. The post-binned and post-skipped pixels are commonly used to form a final image.
Referring to FIG. 1, a diagram of a conventional 3× vertical binning of an initial set 10 of pre-binned pixels to a modified set 12 of post-binned pixels is shown. Each group 14a-14n of twelve pre-binned pixels is converted into a single Bayer set 16a-16n of four post-binned pixels as illustrated.
Referring to FIG. 2, a diagram of a conventional 2× horizontal binning of an initial set 20 of pre-binned pixels to a modified set 22 of post-binned pixels is shown. Each group 24a-24n of eight pre-binned pixels is converted into a single Bayer set 26a-26n of four post-binned pixels as illustrated.
Referring to FIG. 3, a diagram of a conventional 2× horizontal and 2× vertical binning of an initial set 30 of pre-binned pixels to a modified set 32 of post-binned pixels is shown. Each group 34a-34n of eight pre-binned pixels is converted into a single Bayer set 36a-36n of four post-binned pixels as illustrated.
Referring to FIG. 4, a diagram of a conventional 2× horizontal skipping of an initial set 40 of pre-skipped pixels to a modified set 42 of post-skipped pixels is shown. Each group 44a-44n of four pre-skipped pixels is converted into a single Bayer set 46a-46n of four post-skipped pixels as illustrated. The pre-skipped pixels not used to generate the modified set 42 are underlined.
Binning and skipping introduce artifacts. The artifacts generated by skipping are commonly worse than the artifacts generated by binning. Therefore, when a sensor supports binning and skipping, binning is often preferred. Nonetheless, even binning artifacts are substantial.